biology essay

Application Of Electromagnetic Waves For Orchid Pest Control Biology Essay

Published: 23, March 2015

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Abstract- one of the problems in production of Orchid is different kinds of harmful pests. To deal with this problem, an idea of using electromagnetic exposure is proposed. The method is stull being tested, however current results shows promise.

INTRODUCTION

INTERACTIVE relations between various branches of science and technology have improved interdisciplinary fields. In fact, most of the research activities take place somewhere among these branches. Therefore, a specialist from one branch usually can propose novel methods, whenever enters the new field, based on his previous knowledge. In this brief paper, a new idea from electromagnetism to be used in Orchid pest controlling is introduced. With the increase in demand for luxury flowers such as Orchids, the producers are trying to maximize increase in production. However, the pest problem is still unsolvable in many aspects.

Traditional producers used man easy solution to the pest control by traditional chemical sprays. Despite the simplicity of use, these chemical insecticides have many disadvantages such as greenhouse have effect [1]. Conventional heating methods in post-harvest agriculture are impractical because of Orchids sensitivity to temperature and the fact that this kind of heating hents (larvae) both pest and the flower. As a result, some modern techniques such as genetic treatments and some other unconventional methods such as ultrasonic waves and electromagnetic treatments have been suggested. The latter has been suggested for pest control of post-harvest stored products such as rice, fruits and walnuts [1]-[10]. Recently, we suggested it for use in preventing the freezing of agricultural products [11]. Here the idea of using electromagnetic exposure to control pests of Orchid is discussed [11]. This process can be based on interference of biological organization of pests or to teasing those using microwaves to protect the flower.

Orchid Flowers

Orchids are treasured for their showy blossoms that are often quite large and brightly colored. Thus, there are many attentions to them which make them a big trade for producers. Famous Orchids are shown in Fig. 1. In the following Sections, some important information about Orchids is presented [12].

Orchids are normally cultivated for their flowers. There are several types of orchid with different size and colors with the same basic structure. Figure 2 shows the three sepals in the outermost parts of an orchid. In non-orchid flowers this part is green and helps protect the flower when it is still at its bud stage. In orchids, however, they are colored and help to create greater color and size. The uppermost sepal in each flower, normally called the dorsal sepal, is slightly larger than the other two. These two are positioned at each side and towards the base of the flower. The size and shape of these sepals varies greatly from species to species, and industrial florist would like to develop orchids that are larger and have more unique sepals. Also, they have three petals and these are colored petals. The two uppermost petals, on either side of the flower, are equal in size and shape. However, the lower petal is usually formed into the shape of a lip and is known as the labellum. This petal is the most decorative and highly formed part of an orchid flower and frequently acts as a landing platform for pollinating insects. In addition, they mimic insects in and color and shape thus attract them to the flower.

In size, orchid flowers size range from minute types up to 20 cm. Even within a genus, the shapes and sizes of flowers also vary widely. However, the structures of all orchid flowers have the same basic form, irrespective of whether they are of borne on a stem, such as with Pleione formosana, or in clusters on pendulous stems individually, like those of Dendrobium densiflorum. Each flower has three petals and three sepals.

Fig.2: A diagram of the various parts of an Orchid

Cymbidium is one the most famous of Orchids, thus, the cultivation information of this orchid is presented as an example to others. It is superb orchids, with modern ones in a wide color range and spikes that bear 6-20 long-lasting flowers. A Large-flowered type (also known as Standard Cymbidiums) normally blooms from early winter to late spring with flowers lasting 8-12 weeks. Miniature-type flower live from mid-autumn to late spring with flowers lasting 6-8 weeks and sometimes longer. The required temperature is 11 to 14&deg;C (52-57&deg;F) at night and 16-20&deg;C (61-68&deg;F) during the day.

Cymbidiums are sensitive to high temperatures; hence sufficient ventilation is necessary. Additionally, when flower buds are developing it is essential that the temperature at night falls below 15&deg;C.

During early summer to early autumn period, orchids need to be placed in moderate to good light outside or in a cool greenhouse. The plants could slowly acclimatize to outdoor or cool greenhouse conditions in early summer, and slowly to indoor conditions in early autumn. To provide sufficient humidity around the plant, one can place it on moist gravel. However, the base of the pot cannot be constantly soaked.

Also, when watering orchids to the 1st time, its necessary to add a specific fertilizer. for instance, when fertilizers are used excessively and in strong concentrations, damage the roots of an orchid.

Pest of Orchid

Usually, several kinds of pests attack orchids. Thus, it is essential to keep all greenhouses and conservatories clean and free from rubbish and factors that might cowage pest breeding. To control these pests, some insecticides have been used, but it is found that they are hazardous to people and the environment. Some examples of orchid pests are red spider mites, aphids, false spider mites, mealy bugs, scale insects, thrips and weevils as shown in Fig. 3 respectively [12].

Red Spider Mites Aphids False Spider Mites

Mealy Bugs Scale Insects Thrips

Weevils

Fig. 3: Main pests of Orchids

Red Spider Mites

The mites are small insects with the size of a small pinhead and also slow-moving. Red spider mites are minute, eight-legged, spider-like insects. They mainly infest the undersides of leaves, causing the upper surfaces to become speckled with yellow blotches. Severe infestations are very unpleasant and leaves will often fall off the plane. If the problem is ignored, the mites will produce webbing between the leaves arid stems.

In addition, dry atmosphere encourages them where they are more pernicious when plants are insufficiently watered and the compost is constantly dry. Red spider mites are difficult to eradicate once they have become established.

Aphids

Aphids or greenflies are harmful sap-sucking pests which spread quickly if not continued. They gather around the soft parts of shoots especially their tips, junctions of stems and under leaves, sucking sap and causing leaves to those pale. They are green, plump and have tiny shore wings. They secrete a substance which encourages the growth of mold.

False Spider Mites

In recent years, false spider mites have become bothersome, especially the Phalaenopsis species. They cause pitting on the upper surface of leaves which causes fungal disease if neglected. In the beginning of infestation, we use the same control measures as suggested for red spider mites. Although this harmful pest can be controlled, it causes marks on the leaves that are repairable.

Mealy Bugs

Mealy bugs are slow-moving similar to red spider mites. They are gradually clustered and static insects which resemble small woolly woodlice. They congregate around stems, leaf-joints and under leaves. They suck sap and produce a sticky substance which encourages the growth of dirty. Advance infestations are difficult to eliminate and best treated with a systemic insecticide.

Scale Insects

Scale insects look like a small brown disc and are formed on the undersides of leaves, especially along the veins. They are unsightly and cause light spots. They can be removed by wiping with a damp cloth or moist cotton bud when they are still young. Plants which are heavily infected may also exhibit sooty mould. At this stage, eradication is very difficult.

One of the most destructive pests of orchids is weevils. Adult beetles are tiny, less than 12 mm long. They feed on leaves, mainly at night and the creamy-white larvae (grubs) have brown, somewhat large heads with their mouth adapted to eat roots. The larvae live in the compost and hence needs to be changed when repotting to ensure that new plants are free from these pests. Chewed leaves are easily seen but when larvae are present, the first indication of their presence is when the foliage wilts. They cause a severe infestation in this stage. Placing the plant under a shade helps their recovery.

Pest Control Using Electromagnetic Treatment

Electromagnetic waves for insect control in commodities for many years. Initial investigations using RF heating to control pests of grain and nuts were conducted by Frings [13], Thomas [14] and Nelson [15]. Hirose et al. [16] studied the use of dielectric heating (2450 MHz) for controlling tobacco moth larvae.

There are various ideas about the mechanism of pest control using electromagnetic waves. Most of the researchers believe that the waves can only warm up the pests which mostly composed of water rather than the other materials in the region [1-9], but the others say that they may have some unknown impacts which can be useful in the treatment [17]. Below, both ideas are evaluated, but more investigations are in progress.

To warm up a material remotely using radio waves, the imaginary part of the dielectric constant can be used as mentioned in section V. However, the main goal is not just to warm a material (i.e. a flower) indoor since it can be done using a heater or 2.4 GHz microwave source. The mission, here, is to warm a fluid material without affecting the others while the other ones are not affected. This can be done using the differences between the imaginary parts of the dielectric constants which changes versus frequency as well. Section V also furbishes the theory. We believe that there is an appropriate frequency for which the energy is absorbed by the pest but not the home. So this process will not affect the quality of the Orchids, owing to the fact that they are sensitive to temperature increase.

On the other hand, it is said that not only these waves warm the pest, but also they can interfere with their physiology [18]-[21]. To verify this claim, we have done some tests on Sunne pest samples which are pests of wheat. Figure 4 (a)-(b), represents some of our practical tests to find suitable frequencies of the electromagnetic exposure. Figure 4(a) shows pest running away from the antenna in some frequencies. The pest's escaping may be due to warming but the power is not high enough for significant temperature increase. Moreover, we do not expect the waves to attract pests, but some frequency bands will do it. The idea can be extended to Orchid pests as well.

(a) Attraction (b) Repelling

Fig.4: Attraction and repelling phenomena of pest in response to different frequencies.

Electromagnetic Heating

Dielectric materials, such as most plants, can store electrical energy and convert it to heat. Each material has a complex permittivity (ε) in general. According to measurements this value frequency dependent. The imaginary part (ε′′) of this value is responsible for absorption of electromagnetic waves in each material. Eq.(1) shows the general form of the first Maxwell's equation considering (ε′′).

(1)

As a consequence, total power absorption in a specific material is achieved if the second part of the equation is integrated over the material volume as can be seen in Eq. (2).

(2)

The basic idea is to use ε′′ to warm the selected materials far from electromagnetic source.

The increase in temperature of a material by absorbed electromagnetic energy can be expressed in Eq. (3) as stated in [5].

(3)

where C is the specific heat of the material (J.kg-1.&deg;C-1), ρ is the density of the material (kg.m-3), E is the electric field intensity (V.m-1), f is the frequency (Hz), ε is the dielectric loss factor (-) of the material, Δt is the time duration (s) and ΔT is the temperature rise in the material (&deg;C).

The ε parameter varies with frequency. For instance, ε′′ of water has a peak in 2.45 GHz frequency. The absorption frequency of water may help us in warming the water in the insects' body but probably all of the other water-composed materials nearby may absorb the energy as well. A frequency which maximizes the difference between temperature increment in pest and Orchids using the frequency dependent character of ε(f) is required. With the aid of Eq. (3), the Goal function in Eq. (4) represents the problem which should be maximized.

(4)

Using the assumption that specific heat of the both material are equal, Goal function is reduced to Eq. (5).

(5)

If we simply assume that electric field is equal in both pest and Orchid regions, the Goal function is reduced to Eq. (6).

(6)

Therefore, approximately, it can be stated that we are searching for a frequency at which the difference between ε′′ (f) of the pests and Orchid is the most possible value. In order to do this, we are going to measure the effective permittivity of all Orchid pests to find the best frequency in which the difference between ε′′ of the pest and other materials like Orchids is the largest.

Challenging Problems

There are six challenges that need to be overcome for implementation of these ideas: power, health effects, biological effects, price, frequency allocation and design complexity. Power problem is solvable if the applied frequency is not higher than gigahertz. High power sources are now common in VHF and UHF frequencies and cost is affordable. Today, electromagnetic waves are known to pose for health hazards and biological defects such as cancer, but it is reported that lowering the exposure will reduce the hazard. Thus in our method we expose the waves for limited periods which is enough to increase the temperature of pests or products. In spite of the health and, biological effects of electromagnetic exposure ,…… this should be evaluated to ensure that it does not have a harmful effect on the ecosystem.

The problem of frequency allocation could be solved for indoor environment as well. Taking few frequencies to send in probably VHF and for limited days in year is not unachievable; however we can shift our frequency to ISM bands.

The final problem is to design such a plan to warm up pests in different areas. For example if we use a single power source, it will be difficult to use it for terrain uneven train. Thus for each area, this problem should be solved separately and one should design a suitable array of sources to cover the area. Additionally the frequency of treatment must be selected in a manner that the absorption of energy by pest be more than other materials.

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